*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}
h1{
    font-size: 20px;
    color: white;
}

.mecu{
    background-color: gray;
    width: 100px;
    cursor: pointer;
}

li{
    font-size: 12px;
    color: white;
}

.ul{
    display: none;
}

h1:hover{
    background-color: #c0c0c0;
}

.xuan{
    margin-top: 300px;
}


.xuan>li{
     width: 100px;
     height: 40px;
     border: 1px solid black;
     margin-left: 100px;
    color: black;
    font-size: 14px;
    display: inline-block;
    text-align: center;
    padding-top: 10px;
    cursor: pointer;
 }

.xuan>li.on{
    background-color: aqua;
    border-color: aqua;
    color: white;
}

.btn{
    width: 50px;
    height: 30px;
    margin-top: 100px;
}

.link{
    margin-top: 100px;
    cursor: pointer;
}